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ajju 19th July 2004 02:17 PM

[INDIA]Building heavy duty Chasis for Power Amps.
 
2 Attachment(s)
Hi everyone,

As me and Sunil were meandering along the bylanes of SP Road hunting for heatsinks and chasis we struck upon an Idea. Why not buy Al extrusions bars sheets and make them. We got the resources, but the real issue is quantity.
There are various Al extrusions avaialble at SP road, including the ones specifically meant for heatsinks. Anodised, nice rugged and heavy. They sell only as whole bars. (ie 6ft(8kg) or 12 Ft) and the price is 170 INR per Kg for the heatsinks. (these are 100mm wide, with around 6-7mm thick base, 3mm thick fins and a seperation of about 8-10mm between fins..the fins are about 25 mm high..!)
There are 98mm bars available with a thickness ranging from 4mm, 6mm , 8mm...these too are 12 feet long pieces. The cost for a piece was around 960INR.
I've attached a drawing (made in word, so please excuse the quality) of what we propose to do, just one of the ideas..! This is for a multichannel Gainclone.! If we can generate a group order we shall talk to the ppl at the shop. They have contacts to Al worksops who can fabricate this. Rt from cutting, drilling, milling etc etc to anodising or powder coating.

The cost of materials worksout to..

for a chasis similar to the one in the doc...
2feet of heatsink = 340INR, (2.6Kg) (sides)
2Ft 6 inches Al bar = 200INR (1.5kg) (front, back)
2*(1ftx1ft 4inches) = 250-500 (0.5kg-1.5kg depending on thickness) (top and bottom)
-----------------------------------------------------------------------
Total = 800INR - 1250INR (4.6 5.6 kg)

Adding an equal amout for fabrication and knick knacks like L junctions, nuts, etc etc...that would be one hell of a chasis for around 2500INR..!!

Anybody game..!!
If we can get enough ppl, we might get a good bargain on the fabrication costs as well..!!

What do you guys think..?

ajju

tcpip 20th July 2004 10:50 AM

Re: [INDIA]Building heavy duty Chasis for Power Amps.
 
Very interesting stuff. Thanks for the heads-up. I'll try to put in my ten-paise worth of reactions and data points.
Quote:

Originally posted by ajju
There are various Al extrusions avaialble at SP road, including the ones specifically meant for heatsinks. Anodised, nice rugged and heavy. They sell only as whole bars. (ie 6ft(8kg) or 12 Ft) and the price is 170 INR per Kg for the heatsinks. (these are 100mm wide, with around 6-7mm thick base, 3mm thick fins and a seperation of about 8-10mm between fins..the fins are about 25 mm high..!)
Here, the kind of cross-section you describe is available in retail quantities, cut and black anodised, for about Rs.15-16/cm of length. This means that a 12" length will cost me max Rs.480 or so. See pictures here and here in some of my earlier posts. This one is 100mm wide, and has tall fins like you described. I paid Rs.500 or so for a 13" long piece.

In your case, you will get the raw stock at about Rs.225 for 12" (1.33Kg weight), and then you'll have to do the finishing (filing, deburring), and black anodising separately. And anodising is quite expensive, though I don't have ready figures.

I have bought another section which was 7.5" wide (18.5cm or so) for Rs.25/cm length. That one had fins which were slightly shorter (maybe 2cm tall?) and thicker. That's the widest section I've seen at L.Road.

Personally, I think I'd rather pay the extra price and buy ready-made heatsinks retail than go looking for a service provider for each step. And from experience I can tell you that simply transporting stuff from one place to another can eat up money in just fuel costs, tempo fares, auto fares, cab fares, etc. We've spent a few thousand rupees in the last few months in just conveyance of heavy and/or delicate items this way. Once I factor in those costs, the raw-stock option does not appear all that cheap. My friend visited Jeetubhai (Peerless drivers) a fortnight ago, and spent more than Rs.100 on just that visit.

And I'm really surprised that you need to do a bulk purchase for these sections. I have often walked around in shops in New Bombay and picked up one metre of this section and half metre of that for a few rupees. They simply cut a piece from one of the 12ft-long pieces and give it to me. Needless to say, the retail rate is higher than the full-length rate, but who cares?

When we were interacting with Uncle Harry for getting custom-built knobs made, I asked him once about making just 20 pieces of 50mm knobs. He said that this would be very difficult, because Al rods must be bought in 12-ft-long lengths, and so on. Then, in front of me, he called his Al supplier and that guy said that he'd happily sell any length... even a half-metre length. Uncle Harry was surprised but he rapidly confirmed to me that 12-foot-long rods were not needed. This seems to be the universal story.

Quote:

The cost of materials worksout to..

for a chasis similar to the one in the doc...
2feet of heatsink = 340INR, (2.6Kg) (sides)
2Ft 6 inches Al bar = 200INR (1.5kg) (front, back)
2*(1ftx1ft 4inches) = 250-500 (0.5kg-1.5kg depending on thickness) (top and bottom)
-----------------------------------------------------------------------
Total = 800INR - 1250INR (4.6 5.6 kg)

Adding an equal amout for fabrication and knick knacks like L junctions, nuts, etc etc...that would be one hell of a chasis for around 2500INR..!!
Sorry if I'm not sounding too enthusiastic.

I feel that if you actually try to get a few chassis made this way, you'll realise that there are severe problems on two fronts:
  • Quality: you really need to invest time and effort to find a machine shop who will make boxes and chassis with accurate cutouts, with 0.5mm accuracy. Just finding out such a workshop takes a lot of waste of money/time. I've found Dinrack (lucky first time) who are expensive, but who happily take retail orders and do a superb job of finish and accuracy. I've got two chassis, two extra front and back panels, plus two extra large metal plates done from them and they've been perfectly accurate and well finished each time. And I never have to hear their cribs of "we want at least 100 pieces per order."
    My Dinrack experience is not typical. I have friends who are involved in getting prototypes made and other similar activities. All of them confirm that those machine shops which have expensive and accurate tooling are totally unwilling to look at orders less than a hundred or so. The smaller shops will take small orders but will do all cutouts by hand as a result of which dimensional tolerances will be off, holes will not align, and so on. If you can find a machine shop which will give you Dinrack-type accuracy but will work with raw Al stock you supply, then of course you're home free.
  • Incidental expenses: Your cost calculations will change for the worse once you begin to factor in your incidental expenses of running around. Even assuming you do it in a car, not a cab, distances in B'lore are not very small and you'll land up burning plenty of petrol. As I said earlier, the estimate of my friends and me in Bombay is that we must've spent Rs.5000 or more in the last few months on just cab fares and petrol, transporting audio related stuff or making trips to obscure, unreachable industrial estates to get work done.
Of course, if you get something this way which you desperately want but can't get from any other route, then go right ahead. Some people would be shocked to hear we in India are considering getting custom-made knobs for our front panels. :D

Sorry for sounding like a party-pooper. I really appreciate your enthusiasm, don't misunderstand me. If you can address these issues, then go right ahead.

ajju 20th July 2004 01:21 PM

Many thanks Tarun for the long indepth reply..!

here is what I thought..!

Quote:

you'll have to do the finishing (filing, deburring), and black anodising separately. And anodising is quite expensive, though I don't have ready figures.
Re visiting the figures...approx..
500 for a finished black anodised peice..
225 for an unfinished raw piece....!!
That means labour and finishing costs are equivalent to that of the material itself...
That is the rough estimate which I took too..!! So roughly the final product will be twice your material cost.. (accounted)
Next...the fab which will do the work for us...!!
Looking at the design, in its current form all you need is a lot of holes drilled in various sizes. No others shape cutouts needed..We plan to use all MX connectors and stuff...so that would remain a standard across INDIA(if it comes to that) and they are easily available..I would have preferred a handle to be made on the front plate on either side..but that would call for some milling and hence kept it away.. (alternatively we will lookout for some nice industrial grade door handles..either in Al or brushed steel...)I guess any machine shop with a good drill and premarked pieces would be able to drill holes pretty neatly..! then you need L sections cut out to specific lengths to fasten and strengthen the joints...again you need holes drilled and threaded for the purpose.. (One can even consider Araldite...or there was another green coloured varient, which was very common in SPACE industry and they used it for almost everything...!! only thing it was required to be cured in a owen)

Quote:

I have bought another section which was 7.5" wide (18.5cm or so) for Rs.25/cm length. That one had fins which were slightly shorter (maybe 2cm tall?) and thicker. That's the widest section I've seen at L.Road.
Here in bangalore we couldnt find many.!


Quote:

Personally, I think I'd rather pay the extra price and buy ready-made heatsinks retail than go looking for a service provider for each step. And from experience I can tell you that simply transporting stuff from one place to another can eat up money in just fuel
The wholesaler whom we talked to said he has contacts.. A worksop which will do all the stuff..cutting, drilling milling anodising, powder coating etc etc.. he said he could get an estimate if we could give him detailed drawings...but we dint have them then..! Added to that, they provide raw materials to the workshop..So transportation wouldnt be a problem as it can be done alongside a normal order..!
Else there are couple of small workshops within a radius of 100mts from this shop.. so transportation shouldnt be a major ptoblem.!

Quote:

And I'm really surprised that you need to do a bulk purchase for these sections. I have often walked around in shops in New Bombay and picked up one metre of this section and half
Probably we will find them too..need to explore a bit further....
But if we could get say 3-4 orders we could get a slight advantage in bargaining..even if its a small work shop..!

Quote:

Quality: you really need to invest time and effort to find a machine shop who will make

Incidental expenses: Your cost calculations will change for the worse once you begin to
Ofcourse yes..but I guess we can find some one to do this..!!
And since its a minimalist design, quality might be easy to acheive...
Lets c..!!


ajju

ashwin 20th July 2004 04:50 PM

Ajju, I'm certainly interested, because right now it's imerative for me to cover up my gainclones or else I get thrown out of the house ;)

The only problem is, I'm using a dual-mono setup, with the two channel grounds separated and meeting only at the source end. That's why I was thinking of a metal-wood combination for the box, and use a wooden section for the base and back panel so that I can safely bolt the heatsinks/connectors to the wood without shorting the negative supplies or the grounds. Also wood would give it a touch of class, even if it's only veneered MDF ;)

Is part wood part metal construction an option for you?

- Ashwin

roadkill 20th July 2004 05:32 PM

Ajju, this sounds like a terrific idea... in fact, I thought of doing it and actually bought the heatsink extrusions and metal sheet sold at Maruthi metals. They're still collecting dust coz I haven't the time to work on 'em. Besides, I'm leaving for the US to pursue an MS... so that means I'll have to bid my amps and speakers goodbye :bawling:

Tarun's right, you may need access to CNC equipment to get proper angles & stuff. Otherwise, you'll need to find someone who has a lot of experience with regular tools, and they're hard to come by. I tried very hard to find some place which will just cut a rectangular hole in a piece of aluminium sheet (2mm thick). Not a soul would touch it, they looked at the aluminium as though it was transported from the future. Ah well... maybe I was looking in the wrong places, I never tried any place in Peenya. But then I'll bet they will only work with "Large orders", so Ajju, here's your chance! Find enough people for a "group order" of maybe 10-15 and be prepared to sweet talk some machine shop owner to help you out.

Good luck on your chassis project. I only wish I could be around to participate...

tcpip 21st July 2004 03:10 AM

Quote:

Originally posted by ajju
Lets c..!!
Best of luck. I sincerely hope it all works out.

ajju 21st July 2004 08:40 AM

2 Attachment(s)
Ashwin,
I've attached a doc which has another design. Unfortunately its still stuck at the drawing board.!
Its been pending for a while now..!

Roadkill,
Where is Maruthi metals. Did you buy them in bulk or as pieces of required length..!
Yes Peenya is one place to explore..Only trouble i have is the language..Let me see if i can get some one who can understand and speak local language..!
btw...wish u good luck and the very best for ur MS..!

Tarun,
Many thanks for the moral support.:)

ajju

ashwin 21st July 2004 04:20 PM

Ajju,
that design looks good. Only problem is we'll have to find a guy who does aluminium bevelling in small numbers. Or we could use wood for the top and bottom and do the bevelling ourselves.

How come you've mentioned Mahavir Aluminium? Do they have an outlet in Bangalore?

BTW, Maruti metals is in SP road. Just before you enter SP road from the Om-electronics side, there is a lane that branches off to the left, before Om. Take that lane, it's at the beginning of that lane. He's a good chap, I bought extrusions for heatsinks from him. He cut the pieces to the size I wanted.

- Ashwin

ajju 21st July 2004 04:27 PM

Yes, Precisely. Al bevelling is an issue...
Actually i was thinking of using wood or Acrylic to work with..!!
Anyways first i'll see if i can persuade some machine shop to do the job for us. I'll also try some expt getting extrusions from Mahavir..!!

ajju

roadkill 22nd July 2004 08:01 AM

Ashwin told me where Maruthi Metals is. Anyway, I bought the extrusions cut to size, he charges a nominal cutting fee. Be sure to go early in the day, if it's close to getting dark, they may not get it cut for you.

Peenya: I suppose most of them would understand Hindi as well as Kannada.

There are supposed to be some chemical agents one can use to get an anodized surface. Couple that with a wire brush and I think it shd be good.

Thanks for wishing me luck! I'll do my best.


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